This invention relates to filter material and is concerned with both the production and use of the material. Filter materials made of several different fibre types, including fibres with different diameter dimensions are already known in the art. Database WPI Section Ch, Week 198733 Derwent Publications Ltd, London reference AN 1987-231919 discloses a filter material comprising 20-60% active carbon fibre with a diameter less than 15xc3x9710xe2x88x926 m; 10-20% ultra thin glass fibre with a diameter of 0.2-0.5xc3x9710xe2x88x926 m; and 20-70% cellulose fibre. Database WPI Section Ch, Week 198506 Derwent Publications Ltd, London reference AN 1985-034894 discloses a filter material comprising 20% fibres with a diameter 0.1-3xc3x9710xe2x88x926 m eg K titanate fibre; 20% fibres with a diameter 5-15xc3x9710xe2x88x926 m eg polyethylene terephthalate; and 20% fibres with a diameter 20-50xc3x9710xe2x88x926 m eg polyethylene terephthalate. U.S. Pat. No. 4,765,812 discloses a filter material comprising 10-20% of a binder material, and 80-90% of a fibre mixture wherein the fibre mixture comprises 75-95% fibres with a diameter greater than or equal to 20xc3x9710xe2x88x926 m and 5-25% fibres with a diameter less than 3xc3x9710xe2x88x926 m.
Material according to the invention is suitable for both particulate and vapour filtration.
As used herein, the term xe2x80x9cvapourxe2x80x9d includes air and gases.
According to one aspect of the invention, filter material suitable for both particulate and vapour filtration comprises a composite of first and second groups of fibres, the fibres of the first group having a relatively large diameter, and the fibres of the second group having a relatively small diameter.
Typically, the fibres of the first group have a diameter of about 7.0xc3x9710xe2x88x926 m and the fibres of the second group have a diameter of about 0.5xc3x9710xe2x88x926 m.
Also typically, the composite material contains about 70% (by mass) of first group fibres.
The fibres of the first group may comprise carbon fibres the fibres of the second group may comprise glass and/or carbon fibres.
According to a second aspect of the invention, a method of producing filter material of composite form suitable for both particulate and vapour filtration, comprises mixing together with binder, first and second groups of fibres, fibres of the first group having a relatively large diameter and fibres of the second group having a relatively small diameter.
The invention also comprises filter material produced by the foregoing method.
The invention further comprises a respirator provided with a filter unit incorporating the novel filter material.
The various aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein: